Field of the Invention
The present disclosure relates to a liquid crystal display device (LCD), and particularly, relates to a touch screen LCD.
Discussion of the Related Art
Recently, use of a touch screen has been generalized by user's demand to conveniently use electronic devices. In case of an external touch screen panel, there are a tape bonding type, a front surface bonding (i.e., a glass bonding type), a module type, or the like according to methods of attaching a touch sensor substrate onto a liquid crystal panel. The glass bonding type is a method that an optical adhesive is formed on an entire surface of a liquid crystal panel to couple a touch sensor substrate to the liquid crystal panel.
In case of the glass bonding type, a touch screen LCD is manufactured using a lamination process that an optical adhesive is formed on a liquid crystal panel where a thin film transistor (TFT) substrate and a color filter substrate are coupled to each other, and then a pressure is applied to attach a touch sensor substrate to the liquid crystal panel.
First, regarding processes of manufacturing a liquid crystal panel, a column spacer is formed on a black matrix layer of a color filter substrate, then a TFT substrate and the color filter substrate having the column spacer are coated with respective alignment layers, and then the alignment layers are rubbed.
Then, the TFT substrate and the color filter substrate are each cleaned, then a seal pattern is formed on peripheral portions of the TFT substrate, and then liquid crystal are dispensed on a predetermined region on the TFT substrate.
The color filter substrate not having liquid crystal thereon is overturned to face the TFT substrate, then the color filter substrate and the TFT substrate are pressurized and coupled, and then the seal pattern is hardened.
The column spacer is formed such that the column spacer is fixed to the color filter substrate and contacts the TFT substrate. In this case, when swiping across a surface of an LCD, there occurs a touch defect that brightness of the swiped portion is not uniform and a spot happens, and when pressing a surface of an LCD with a constant force, there occurs a press defect that a color filter substrate or TFT substrate is deformed and a spot occurs at the pressed portion.
To solve the above problems, a LCD is developed recently, which includes a gap column spacer contacting a TFT substrate and a press column spacer spaced apart from the TFT substrate, which are formed between a color filter substrate and a TFT substrate, to prevent a touch defect and a press defect.
According to densities of column spacer in an liquid crystal panel, a cold bubble phenomenon or gravity defect phenomenon occurs.
The cold bubble phenomenon is caused by a difference between a volumetric shrinkage rate of liquid crystal and a volumetric shrinkage rate of glass used for a substrate according to a temperature drop. Since the volumetric shrinkage rate of liquid crystal is greater than that of glass, the phenomenon occurs that an empty space happens between two substrates. This phenomenon occurs when a density of a gap column spacer is high.
The gravity defect phenomenon occurs because a volume of a liquid crystal layer in a liquid crystal panel increases as temperature rises. A cell gap of the liquid crystal panel becomes greater than a gap column spacer, and the phenomenon occurs that liquid crystal moves down due to gravity. This phenomenon occurs when a density of a gap column spacer is low.
FIG. 1 is a schematic view illustrating a density of a gap column spacer of a liquid crystal panel having a first substrate and a second substrate coupled to each other according to the related art, and FIG. 2 is a view illustrating a touch screen LCD having a third substrate and a liquid crystal panel coupled to each other through a lamination process according to the related art.
Referring to FIG. 1, a liquid crystal panel 10 includes a first substrate 11 which includes a plurality of pixels defined by gate and data lines crossing each other and each including a TFT, a second substrate 20 which includes a color filter and black matrix and on which a gap column spacer 30 and a press column spacer 35 are formed, and a liquid crystal layer 40 between the first and second substrates 11 and 20.
In a state that the liquid crystal panel 10 is not coupled with a third substrate (80 of FIG. 2) including a touch sensor through a lamination process, in order to prevent a cold bubble phenomenon and a gravity defect phenomenon of the liquid crystal panel 10 itself, it is enough for the gap column spacer 30 to be formed to have a density of 0.03% with respect to a display region of the liquid crystal panel 10.
For the purpose of explanations, in FIG. 1, a density or a number of the gap column spacer 30 are not shown exactly, and instead, one gap column spacer 30 is shown in a meaning that a density of the related art gap column spacer 30 is less than that of a gap column spacer (130 of FIG. 4) of an embodiment of the present disclosure.
Referring to FIG. 2, the related art touch screen LCD 110 is manufactured by coupling a third substrate 80 having a touch sensor with the liquid crystal panel 10 using an optical adhesive 60 therebetween. A seal pattern 50 is formed between edge portions of the first and second substrates 11 and 20 of the liquid crystal panel 10.
A cell gap of the liquid crystal panel 10 including the first and second substrates 11 and 20 is reduced by a pressure that is applied in a lamination process to couple the third substrate 80 with the liquid crystal panel 10, and then, after a period of time, the second substrate 20 receives a first tension F1 in a direction to the third substrate 80 by the third substrate 80 coupled to the second substrate 20, and receives a second tension F2 in a direction to the first substrate 11 by the gap column spacer 30 formed on the second substrate 20.
The first tension F1 is a force that the third substrate 80 attracts the second substrate 20 due to the coupling of the third substrate 80 with the second substrate 20 through the optical adhesive 60, and the second tension F2 is a force to maintain the attachment of the second substrate 20 and the first substrate 11 through the gap column spacer 30.
The first tension F1 is smaller at a center portion than at a peripheral portion, and the second tension F2 increases in proportion to a density or a number of the gap column spacer 30.
Accordingly, when a gap column spacer is formed at the density of the related art and a lamination process to couple the liquid crystal panel 10 with the third substrate 80 is conducted, a peripheral portion of the second substrate 20 receives the first tension F1 greater than the second tension F2 and thus moves upward. Thus, a cell gap of the liquid crystal panel 10 at the peripheral portion is greater than that at the center portion.
When the cell gap of the liquid crystal panel 10 becomes greater, liquid crystal moves to a peripheral portion of the liquid crystal 10 having the greater cell gap, thus a transmittance of liquid crystal changes at the peripheral portion, and thus a yellowish phenomenon happens.